Light travels in a zero-index medium without accumulating a spatial phase,resulting in perfect spatial coherence.Such coherence brings several potential applications,including arbitrarily shaped waveguides,phase-misma...Light travels in a zero-index medium without accumulating a spatial phase,resulting in perfect spatial coherence.Such coherence brings several potential applications,including arbitrarily shaped waveguides,phase-mismatch-free nonlinear propagation,large-area single-mode lasers,and extended superradiance.A promising platform to achieve these applications is an integrated Dirac-cone material that features an impedance-matched zero index.Although an integrated Dirac-cone material eliminates ohmic losses via its purely dielectric structure,it still entails out-of-plane radiation loss,limiting its applications to a small scale.We design an ultra-low-loss integrated Dirac cone material by achieving destructive interference above and below the material.The material consists of a square array of low-aspectratio silicon pillars embedded in silicon dioxide,featuring easy fabrication using a standard planar process.This design paves the way for leveraging the perfect spatial coherence of large-area zero-index materials in linear,nonlinear,and quantum optics.展开更多
We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior.Our twisted bilayer photonic device,which has an operating wavelength in the C-b...We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior.Our twisted bilayer photonic device,which has an operating wavelength in the C-band of the telecom window,uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer.We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure,which exhibits a flat band over the entire Brillouin zone.This flat band causes the group velocity to approach zero and introduces light localization,which enhances the electromagnetic field at the expense of bandwidth.Using our original plane-wave continuum model,we find that the photonic system has a larger band asymmetry.The band structure can easily be engineered by adjusting the device geometry,giving significant freedom in the design of devices.Our work provides a fundamental understanding of the photonic properties of twisted bilayer photonic crystals and opens the door to the nanoscale-based enhancement of nonlinear effects.展开更多
基金The authors would like to thank Shahin Firuzi and Olivia Mello for discussions.We acknowledge support from the National Natural Science Foundation of China(62075114).This work is supported by the Center of High Performance Computing,Tsinghua University.
文摘Light travels in a zero-index medium without accumulating a spatial phase,resulting in perfect spatial coherence.Such coherence brings several potential applications,including arbitrarily shaped waveguides,phase-mismatch-free nonlinear propagation,large-area single-mode lasers,and extended superradiance.A promising platform to achieve these applications is an integrated Dirac-cone material that features an impedance-matched zero index.Although an integrated Dirac-cone material eliminates ohmic losses via its purely dielectric structure,it still entails out-of-plane radiation loss,limiting its applications to a small scale.We design an ultra-low-loss integrated Dirac cone material by achieving destructive interference above and below the material.The material consists of a square array of low-aspectratio silicon pillars embedded in silicon dioxide,featuring easy fabrication using a standard planar process.This design paves the way for leveraging the perfect spatial coherence of large-area zero-index materials in linear,nonlinear,and quantum optics.
文摘We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior.Our twisted bilayer photonic device,which has an operating wavelength in the C-band of the telecom window,uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer.We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure,which exhibits a flat band over the entire Brillouin zone.This flat band causes the group velocity to approach zero and introduces light localization,which enhances the electromagnetic field at the expense of bandwidth.Using our original plane-wave continuum model,we find that the photonic system has a larger band asymmetry.The band structure can easily be engineered by adjusting the device geometry,giving significant freedom in the design of devices.Our work provides a fundamental understanding of the photonic properties of twisted bilayer photonic crystals and opens the door to the nanoscale-based enhancement of nonlinear effects.
